Flexible skirting assemblies for ground effect machines



R. S. JONES March 24, 1970 FLEXIBLE SKIRTING ASSEMBLIES FOR GROUND EFFECT MACHINES 3 Sheets-Sheet 1 Filed Jan. 18, 1968 o 0 n\ 0 L 0 V 0 r rrrrrrrrrrrrrrrfrrrr FIG. 1

March 24, 1970 R. s. JONES 3,502,168

FLEXIBLE SKIRTING ASSEMBLIES FOR GROUND EFFECT MACHINES Filed Jan. 18, 1968 3 Sheets-Sheet 2 Man}! 24, 970 R. s. JONES 3,502,163

FLEXIBLE SKIRIING ASSEMBLIES FOR GROUND EFFECT MACHINES Filed Jan. 18, 1968 3 Sheets-Sheet 3 FIGS United States Patent US. Cl. 180127 9 Claims ABSTRACT OF THE DISCLOSURE A flexible skirt for a ground eflect machine, the skirt consisting of an upper hollow flexible member inflated to a desired pressure and a lower part consisting of a plurality of independent flexible segments, the lower part depending from the upper part. Air flows from the upper member to generate and maintain the air cushion and is directed so that a portion flows downwardly into the segments and the remainder flows inwardly directly into the air cushion area, the division of air from the upper member to either the segments or to the air cushion area being governed by the size of the orifices through which the air is ejected. The height of the segments should be within the range 45 to 55% of the total height of the flexible skirt assembly, and preferably, 50%. The width of each segment should be within the range of A and /2 of the vertical height of the segment.

This invention relates to ground effect machines having flexible skirt assemblies to act as barriers to the dissipation of one or more pressurised fluid cushions by which the machine is supported. More particularly it relates to improvements in such flexible skirt assemblies.

It is an object of the invention to provide for such a skirt assembly correlations between the height of the segments and the total height of the skirt assembly and between the height and width of each segment.

According to the invention I provide a ground eifect machine having a flexible skirt assembly which acts as at least part of a barrier to restrict the dissipation of at least one pressurised fluid cushion by which the machine is supported, the skirt assembly including an upper hollow flexible member inflated to a desired pressure, and a lower part made up of a plurality of contiguous segments, wherein the height of at least some of the segments is between 45% and 55% of the total height of the flexible skirt assembly.

A flexible barrier for a fluid cushion should have a freely moving, low drag, lower portion, merging gradually into a stiffer upper portion. This is achieved in the skirt assembly disclosed in this invention by having an upper flexible inflated member and lower segments. The lower tips of the segments, being furthest from the segment supports, have more freedom of movement than the upper parts of the segments. The upper parts of the segments have more freedom of movement than the upper inflated member in which the pressurisation adds to its stiffness.

The upper member, besides being part of the barrier, acts as a settling chamber to give an even distribution of fluid flow to the segments and the fluid cushion. The upper member also provides a base for the attachment of the segments.

If the upper member is too small in relation to the overall skirt height, uniformity of fluid flow to the fluid cushion is not achieved, resulting in lack of stability of the ground effect machine and irregular skirt characteristics. Further, a relatively small upper member may not provide a base adequate to support the proportionally larger segments.

3,502,168 Patented Mar. 24, 1970 If, however, the height of the segments is small compared to the overall skirt height, there is a tendency for the upper member to contact the water, assuming the machine to be operating over water, and, as the upper member is more rigid, the hydrodynamic drag of the skirt assembly is increased.

It has been discovered that a skirt assembly in which the height of the segments is within the range 45% to 55% of the total height of the assembly gives relatively eflicient performance, the best performance being given at 50% The total height of the skirt assembly is defined as the vertical distance between the underside of the rigid structure of the machine and the lowest tip of the flexible skirt assembly when the machine is in its operating condition.

When the skirt assembly is acting as a barrier to the fluid cushion the outer part of each segment takes the form of half a cylinder, and the segment derives its stiflness from the thickness of the material from which it is made, the fluid cushion pressure which inflates the half cylinder and the diameter of the half cylinder. The material thickness is dictated by its rate of wearing and the cushion pressure is dependent upon many variable factors, such as the all up weight of the machine, the loading of the machine, the operating conditions, etc. Thus, the stiflness of the segments is governed by the diameter of the half cylinder, or, expressed in another way, by the width of the segment, this width being normal to the longitudinal axis of the segment.

If the segment is wider than half the vertical distance between the lowest part of the upper member to which it is attached and the lowest part of the segment, it will have unnecessary stiffness, and may develop unnecessary hydrodynamic drag. Alternatively, if a segment is narrower than one quarter of the vertical distance hereinbefore mentioned it will be too flexible, and once bent by rubbing on the surface over which the machine is operating, it will not have suflicient resilience to regain its correct operating position. Therefore, the width of the segments should be within the range of one quarter and one half of the vertical distance between the lowest part of the uper member to which it is attached and the lowest part of the segment.

The segments may be supported by, and depend from, the uppper member, or they may be supported in part by the upper member and in part by other structure of the machine. Such other structure may be flexible or rigid.

The segments may include an outer cushion barrier part, concave towards the fluid cushion area and side parts extending inwards into the fluid cushion area. The side parts of the segments may be oblique to, or at right angles to, the longitudinal axis of the machine, or they may be at right angles to a line representing the boundary of each fluid cushion.

The upper hollow flexible member may be inflated by a fluid supplied by one or more lift fans and the fluid employed may be air. The upper hollow flexible member may act as part of a duct for conveying pressurised air from the lift fan or fans to the air cushion area, and the pressurised air may be injected into the air cushion area by way of apertures in the walls of the hollow flexible member. A first set of apertures may be positioned in the upper part of the inner wall of the hollow flexible member, so that a first portion of pressurised air goes inwardly directly into the air cushion area and a second set of apertures may be positioned in the lower part of the hollow flexible member, coincident with the segments, so that a second portion of the pressurised air goes downwards into the segments and thence into the air cushion area.

The pressure in the upper hollow flexible member may be governed by the total area of the first and the second sets of apertures in relation to the capacity of the lift fan or fans, and the division of the first and second portions of pressurised air may be regulated by the relative sizes of the first set and the second set of apertures.

The segments may taper over whole or part of their length, and they may be partly or completely closed on the air cushion side.

The invention will now be described, by way of example, with reference to the accompanying drawings, in which:

FIGURE 1 is an inverted plan of a flexible skirt assembly according to the invention. It should be noted that in order to improve the clarity of the figure, the number of segments drawn is less than the actual number provided,

FIGURE 2 is a perspective view looking forward from the underside of the machine at a section of the skirt assembly on the port side of the machine, and

FIGURE 3 is a perspective view of part of one of the segments of the flexible skirt assembly.

Referring first to FIGURES 1 and 2, there is shown a ground effect machine having a rigid base platform which includes a buoyancy chamber 11 provided with a flexible skirt assembly. The flexible skirt assembly consists of an upper hollow flexible member 12 attached, by suitable releasable fastenings, to the rigid base platform at points 13 and 14 and segments 15 depending from the upper hollow flexible member 12. The member 12 is inflated to a predetermined pressure by air from lift fans (not shown) conducted to the member 12 by ducts 16. The member 12 has orifices 17 in the upper part of the wall adjacent to the air cushion area 18 and orifices 19 in its lowest part, which feed pressurised air to the air cushion area. The predetermined pressure in the member 12 is governed by the total area of all the orifices 17 and 19 in relation to the output of pressurised air from the lift fans.

Referring now to FIGURE 3, each segment 15 is made up of a sheet of flexible impermeable material folded and arranged beneath the member 12, so that it has an outer part 20 concave towards the air cushion area 18 and side parts 21 extending into the air cushion area. The segments 15 are arranged below the member 12 (FIGURE 2) in side by side relationship, and, as they are open to the cushion area, the cushion pressure in each segment causes the side parts 21 to bear against the neighbouring side parts to form a seal, while the outer parts 20 form an air cushion barrier. The segments 15 are arranged so that the side parts 21 are at right angles to a vertical plane representing the boundary of each air cushion or at any other convenient angle.

To provide an efficient flexible skirt assembly the height of the segments 15, represented by the distance H in FIGURE 3, is within the range 45% to 55% of the total height of the skirt assembly. Preferably the height of the segment is 50% of the total height of the skirt assembly.

Each segment 15 is constructed so that its width, represented by the distance W in FIGURE 3, is within the range one quarter to one half the height (H) of the segment.

The stern skirt 22 and the lateral stability barrier 23 (FIGURE 1) may be of the form disclosed in the present invention, or they may be of any other suitable form.

I claim as my invention:

1. A ground effect machine having a flexible skirt assembly which acts as at least part of a barrier to restrict the dissipation of at least one pressurized fluid cushion by which the vehicle is supported, the skirt assembly including an upper hollow flexible member inflated by air supplied by at least one lift fan to a desired pressure and a lower part made up of a plurality of contiguous segments, wherein the height of at least some of the segment is in the range between 45% and 55% of the height of the flexible skirt assembly and wherein air is supplied to the air cushion area by way of a first set of apertures positioned in the upper part of the inner wall of the hollow flexible member and a second set of apertures positioned in the lower part of the hollow flexible member coincident with the segments.

2. A ground effect machine as claimed in claim 1, wherein the height of at least some of the segments of the skirt assembly is 50% of the total height of the skirt assembly.

3. A ground effect machine as claimed in claim 1, wherein the width of the segments is between one-quarter and one-half of the vertical distance between the lowest part of the upper member and the lowest part of the segment.

4. A ground effect machine as claimed in claim 3, wherein at least some of the segments of the skirt assembly are supported in part by the upper member and in part by the upper member and in part by the rigid structure of the machine.

5. A ground effect machine as claimed in claim 4, wherein at least some of the segments of the flexible skirt assembly include an outer cushion barrier part concave towards the fluid cushion area and side parts extending into the fluid cushion area, the side parts being oblique to the longitudinal axis of the machine.

6. A ground efi'ect machine as claimed in claim 4, wherein at least some of the segments of the flexible skirt assembly include an outer cushion barrier part concave towards the fluid cushion area, and side parts extending into the fluid cushion area, the side parts being at right angles to a line representing the boundary of the fluid cushion.

7. A ground effect machine as claimed in claim 1, wherein the division of a first portion of pressurised air going through the first set of apertures and a second portion of pressurised air going through the second set of apertures is regulated by the relative sizes of the first set and the second set of apertures.

8. A ground effect machine as claimed in claim 7, wherein at least some of the segments taper over at least part of their length.

9. A ground effect machine as claimed in claim 8, wherein at least part of the segments are closed on the air cushion side.

References Cited UNITED STATES PATENTS 3,362,500 1/1968 Bliss l-l'28 3.38:1,197 5/1968 Bingham et al. 1530-428X 3,397,753 8/1968 Hunt of al. l80-127 A. HARRY LEVY, Primary Examiner s. 01. X.R, 1s0 124 

